Reducing fuel consumption of an internal combustion engine is one means to increase overall efficiency. Fuel consumption and thus efficiency pose a problem in particular in the case of Otto-cycle engines, or applied-ignition internal combustion engines. One option for optimizing the combustion process includes using a partially variable valve drive, perhaps in combination with direct fuel injection.
Valve drives are known in which both the lift of the valves and also the control timing are invariable. However, these parameters have an influence on the combustion process, and thus on fuel consumption, and can be varied to a greater or lesser extent by using variable valve drives. For example, if the closing time of the inlet valve and the inlet valve lift can be varied, the adjustments allowing for throttle-free and thus loss-free load control. The mixture mass or charge air mass which flows into the combustion chamber during the intake process is then controlled not by means of a throttle flap but rather by means of the inlet valve lift and the opening duration of the inlet valve. Variable valve drives are however expensive. A further approach to a solution for dethrottling an Otto-cycle engine is offered by cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges.
One concept for reducing fuel consumption, also in the case of diesel engines, is cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges. However, because in the case of constant engine power the deactivation of at least one cylinder of a multi-cylinder internal combustion engine increases the load on the other cylinders that are still operational, such that said cylinders operate in regions of higher loads, in which the specific fuel consumption is lower. The load collective in part-load operation of the diesel engine is shifted toward higher loads
The inventors have recognized issues with such approaches and herein describe a system and methods for a turbocharged engine, comprising powering the engine using a first operating cylinder, supplementing the power using a second switchable cylinder, the second switchable cylinder switched based on load, the second switchable cylinder being deactivated responsive to a load below a first threshold and activated responsive to the load exceeding the first threshold, and closing a first shut-off valve downstream of a compressor during the partial deactivation.
In one exemplary embodiment, a bypass line is included in a second exhaust line along with a second shut-off element that is opened during the partial deactivation. In this way, the technical result is achieved that the compressor of the second exhaust-gas turbocharger is separated from the rest of the intake system, that is to say deactivated, during the partial deactivation, which prevents the first compressor of the first exhaust-gas turbocharger from imparting a delivery action into the second compressor during the partial deactivation. In addition, the bypass line further serves as a short-circuit line, which is included to eliminate a risk of the second compressor from imparting a delivery action against the closed first shut-off element when the overall intake line is closed. The cylinders which remain in operation during the partial deactivation furthermore exhibit enhanced mixture formation owing to the greater air mass or mixture mass supplied. Further advantages with regard to efficiency are attained in that a deactivated cylinder, owing to the absence of combustion, does not generate any wall heat losses owing to heat transfer from the combustion gases to the combustion chamber walls.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.